#define _CRT_SECURE_NO_WARNINGS 1

#include <stdio.h>
int f(int n)
{	
	int s=0;
	if (n == 0)return 0;
	if (n == 1)return 1;
	if (n == 2)return 2;
	s = f(n - 1) + f(n - 2);
	return s;
}


int main()
{	
	int n;
	scanf("%d", &n);
	f(n);
	printf("%d", f(n));
	return 0;
}